1. Field of the Invention
The present invention generally relates to a method and apparatus for acquiring a channel in radio packet-type data communication which is employed in mobile communications such as a cellular phone system. More particularly, the present invention relates to a method and apparatus for acquiring a channel in radio packet-type data communication, in which the transmission status of a mobile terminal using a given channel, is monitored such that, when the monitored terminal is silent and the channel is unused, packets of data are transmitted over the channel. The present invention makes communications systems more efficient by transmitting packet-type data during periods when channels are otherwise unused (e.g., so-called "silent periods").
2. Description of the Related Art
As transmission information becomes more complex and with the wider use of multimedia, information must be transferred more efficiently. Additionally, when radio data communication is performed between a mobile terminal and a base station, a packet-type communication system is used for effectively utilizing a limited number of radio channels so as to minimize communication cost and to serve more users.
For example, a typical packet-type communication system is a Cellular Digital Packet Data (CDPD) system. The CDPD system includes a CDPD base station, which can be used with a base station for a cellular phone system now in service. The CDPD base station identifies (and assigns) radio channels which are not used for voice communication, and transmits data packets over the unused channels. Thus, radio channels not being used for voice communication are selectively used for data communication.
In such a system, voice communication is given preference in utilizing the radio channels. Thus, if a request exists to use a channel for voice communication, the data communication concedes the channel to the voice communication. Hence, even if a channel is being used for data communication, upon a request for a mobile voice unit, the data communication is terminated, and must wait for another channel to become available (or "hops" to another channel if one is available).
FIG. 9(a) is a block diagram of a packet-type transmitter, and FIG. 9(b) is a block diagram illustrating the operation of the packet-type transmitter.
In operation, a use channel control section 7 controls which channels are used for data transmission based on channel state information (e.g., information regarding which channels are not being used for voice communication). A receiver section 1 indicates which channels are not being used. A switch 5 performs an ON-OFF switching operation, under the control of the channel control section 7, to control whether voice information or packet-type data is transmitted over a given channel.
As shown in FIG. 9(b), in step 30 the operation begins with a request for a packet-type data transmission being made to the base station. In block 31, a determination is made as to whether there is an unused channel assigned by the base station. In other words, it is determined whether an available channel (e.g., a channel not being used by another mobile unit) exists. If there is no available channel, the process returns to step 30 to again request a packet-type data transmission.
If a channel is available, in step 16, packet transmission is started. In step 32, it is determined whether a mobile voice station requests the channel being used for packet-type data transmission and more specifically whether a voice call currently uses the channel. If "YES" in step 32, processing proceeds to step 33, and a search is begun for a different available channel. If there is no voice request (e.g., a "NO" in step 32), the processing proceeds to step 18, where the packet-type data transmission is completed, and the process terminates.
In conventional packet-type data communication systems, voice communication is given preference, and a channel is used exclusively for voice or exclusively for data (e.g., conventional systems do not share voice and packet-type data on the same channel). Therefore, with conventional systems, if all of the available channels are transmitting voice communication, data cannot be transmitted. This is a problem and lowers system efficiency.
Hence, if a voice communication (for example, a cellular telephone call) is in progress, the channel used by the cellular phone cannot be used to transmit data packets during the entire length of the call (or during the time that the cellular phone remains within a given cell). Further, the channel is reserved for voice communication upon receiving a request for connection for voice communication. In conventional systems, voice communication dominates the channel availability, regardless of whether actual voice bursts are being transmitted and received. Therefore, the conventional system does not use the "dead air" time (e.g., the time period between words or other silent periods of voice communication, or the time after a request for voice channel connection is received but no actual voice communication is occurring) to transmit data or other signals.
Additionally, if a channel is being used for the packet-type data communication, it will be interrupted and terminated if there is a request for voice communication. The above-mentioned problems result in the conventional systems having poor efficiency.
JPA 2-117227 discloses the general concept of transmitting data packets over the voice channel. However, for data communication, JPA '227 uses/requires an idle (e.g., vacant) channel not being used for voice communication. It cannot transmit packet data during a silent period in a channel being used for voice communication.